The process which makes major difference between ${C_3}$ and ${C_4}$ plants is
(A) Respiration
(B) Glycolysis
(C) Calvin cycle
(D) Photorespiration

Hint: ${C_3}$ plants use Calvin cycle in the dark phase of photosynthesis. The first stable intermediate product is phosphoglyceric acid; it is a $3$ carbon containing acid. ${C_4}$ plants use a hatch-slack pathway during dark reaction and the first stable product is $4$ carbon acid compound called oxaloacetate.

Complete Answer:
The process which makes a major difference between ${C_3}$ and ${C_4}$ plants is called photorespiration.
(A) Respiration: The process in which the complex food material breaks down into simpler form with the release of energy and carbon dioxide is called respiration. There are two types of respiration namely aerobic and anaerobic respiration when respiration takes place in presence of air (oxygen), It is called anaerobic respites.
(B) Glycolysis: The process by which one molecule of glucose is converted into two molecules of pyruvate with the release of two hydrogens and two molecules of water is called glycolysis.
(C) Photorespiration: The process in which the oxygenation of RuBP takes place in the presence of enzyme RuBisco is called as photorespiration. in \[{C_4}\] plants, photorespiration does not occur this is because plants have mechanism that increase the carbon dioxide concentration at the site of enzyme. Thus, ${C_4}$ plants have better productively yield than ${C_3}$ plants.
(D) Calvin cycle: The process by which conversion of carbon dioxide into sugar takes place is called the Calvin cycle. This cycle is performed by algae and many plants.

Therefore, from above explanation correct option (C) Photorespiration.

Note: The importance of glycolysis is as follows,
- It has a role in oxidising hexoses to provide ATP.
- It also helps in producing precursors for anabolism.
- It can occur in both cytosol and plastids of photosynthetic and non photosynthetic parts.